A variety of refrigerant compressors for use in vehicle air conditioning systems are currently available. One popular vehicle compressor design is the radial compressor. Advantageously, radial compressors are relatively compact and lightweight when compared to, for example, variable displacement axial compressors. More particularly, the radially extending pistons occupy a minimum axial length. Accordingly, the compressor housing may be both smaller in size and lighter in weight. This makes the radial compressor particularly suited for utilization in compact vehicles. This is because such vehicles have very limited space within the vehicle engine compartment to accommodate a compressor. This is particularly true with today's vehicles that also incorporate relatively low hood lines for better aerodynamics.
A radial compressor is shown in, for example, U.S. Pat. No. 3,924,968 to Gaines et al, entitled, "Radial Compressor with Muffled Gas Chambers and Short Stable Piston Skirts and Method of Assembling Same", issued Dec. 9, 1975 and assigned to the assignee of the present invention. The disclosure of this patent is incorporated herein by reference.
As shown in the Gaines et al patent, a radial compressor typically includes a rigid cast cylinder housing closed by a cylindrical shell. One pair of oppositely extending cross bores are provided in the housing on a first axis. A second pair of cross bores are provided in the housing on a second axis normal to the first axis.
A piston assembly is received for reciprocal movement in each cross bore. The outer end of each cross bore is closed by a valve assembly including an annular discharge reed plate that controls refrigerant flow through a series of circumferentially spaced discharge apertures. More particularly, the reed plate controls the flow of pressurized gas from the cross bores into an annular discharge chamber.
A drive shaft is supported for rotation on bearings held in the housing. The shaft includes an eccentric driver including a slider block mounted for relative rotation thereon. In operation, rotation of the shaft results in reciprocating movement of the slider block along the two axes to provide reciprocation of the piston assemblies within their respective cross bores. Movement of one piston assembly within its respective cross bore toward the center of the housing causes low pressure refrigerant gas to feed into the bore through a suction reed plate. The opposing piston assembly is simultaneously extended into the opposite cross bore to compress refrigerant gas previously drawn in on its suction stroke. At the proper time and pressure the discharge reed plate opens so that the high pressure gas flows through the apertures in the valve assembly and into the annular discharge chamber. The pressurized refrigerant gas then flows around the discharge chamber mixing in turn with the high pressure gas from the other cylinder bores. A single discharge port in the chamber between two of the cylinders feeds the combined high pressure gas supply to the air conditioning system. The low pressure or spent refrigerant gas returning from the system is recirculated to the compressor through an inlet port in the central section of the housing.
The formation and propagation of high pressure pulsations is a naturally occurring byproduct of compressors of this type. These pulsations are in effect pressure waves in the pressurized refrigerant. If not dampened, these pressure pulsations cause rough operation, and induce significant vibrations in the vehicle that cause an unpleasant sensation to the occupants. This results not only an annoyance, but also is indicative of inefficient compressor operation.
Further, there is a significant noise problem associated with these pressure pulsations within the compressor. It has been found that the noise can even propagate through the connecting lines to the evaporator unit inside the vehicle, where it can be particularly annoying to the occupants. It is believed that in certain air conditioning system installations, the pulsations can even excite other of the system components causing additional sources of vibration and significantly increasing the noise. The vibrations if left unchecked can even lead to premature fatigue and failure of component parts throughout the air conditioning system, but especially within the compressor.
Various attempts have been made to attenuate these pressure pulsations in order to provide smoother and quieter running systems. Many incorporate mufflers that are positioned in the pressurized refrigerant discharge line leading from the compressor discharge port to the condenser unit of the air conditioning system. Such a muffler typically takes the form of a restricted orifice that operates as a flow control device limiting the rate at which pressurized refrigerant is permitted to pass through the refrigerant line. The resulting restriction of refrigerant flow serves to dampen pulsations to a limited extent.
Thus, while relatively effective for this purpose, such mufflers do not provide the best solution to the problem. More particularly, while maintaining the back pressure and heat generation at an acceptable level, the pulsation attenuation that can be gained is limited. Several attempts have been made in the past to change the physical structure of the muffler/restricted devices, but with limited success. Contrary to these previous attempts at redesign of existing devices, we have discovered that pulse attenuation can be more effective if provided at spaced locations around the discharge chamber. Thus, improvement in this direction is the focus of the present invention.